1 /*
2 * Copyright Amazon.com Inc. or its affiliates. All Rights Reserved.
3 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
4 *
5 * This code is free software; you can redistribute it and/or modify it
6 * under the terms of the GNU General Public License version 2 only, as
7 * published by the Free Software Foundation.
8 *
9 * This code is distributed in the hope that it will be useful, but WITHOUT
10 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
11 * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
12 * version 2 for more details (a copy is included in the LICENSE file that
13 * accompanied this code).
14 *
15 * You should have received a copy of the GNU General Public License version
16 * 2 along with this work; if not, write to the Free Software Foundation,
17 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
18 *
19 * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
20 * or visit www.oracle.com if you need additional information or have any
21 * questions.
22 *
23 */
24
25 #include "precompiled.hpp"
26 #include "gc/shenandoah/shenandoahCardTable.hpp"
27 #include "gc/shenandoah/shenandoahHeap.inline.hpp"
28 #include "gc/shenandoah/shenandoahUtils.hpp"
29 #include "runtime/init.hpp"
30 #include "services/memTracker.hpp"
31
32 void ShenandoahCardTable::initialize() {
33 size_t num_cards = cards_required(_whole_heap.word_size());
34
35 // each card takes 1 byte; + 1 for the guard card
36 size_t num_bytes = num_cards + 1;
37 const size_t granularity = os::vm_allocation_granularity();
38 _byte_map_size = align_up(num_bytes, MAX2(_page_size, granularity));
39
40 HeapWord* low_bound = _whole_heap.start();
41 HeapWord* high_bound = _whole_heap.end();
42
43 // TODO: Why rs_align is 0 on page_size == os::vm_page_size?
44 // ReservedSpace constructor would assert rs_align >= os::vm_page_size().
45 const size_t rs_align = _page_size == os::vm_page_size() ? 0 : MAX2(_page_size, granularity);
46
47 ReservedSpace write_space(_byte_map_size, rs_align, _page_size);
48 initialize(write_space);
49
50 // The assembler store_check code will do an unsigned shift of the oop,
51 // then add it to _byte_map_base, i.e.
52 //
53 // _byte_map = _byte_map_base + (uintptr_t(low_bound) >> card_shift)
54 _byte_map = (CardValue*) write_space.base();
55 _byte_map_base = _byte_map - (uintptr_t(low_bound) >> _card_shift);
56 assert(byte_for(low_bound) == &_byte_map[0], "Checking start of map");
57 assert(byte_for(high_bound-1) <= &_byte_map[last_valid_index()], "Checking end of map");
58
59 CardValue* guard_card = &_byte_map[num_cards];
60 assert(is_aligned(guard_card, _page_size), "must be on its own OS page");
61 _guard_region = MemRegion((HeapWord*)guard_card, _page_size);
62
63 _write_byte_map = _byte_map;
64 _write_byte_map_base = _byte_map_base;
65
66 ReservedSpace read_space(_byte_map_size, rs_align, _page_size);
67 initialize(read_space);
68
69 _read_byte_map = (CardValue*) read_space.base();
70 _read_byte_map_base = _read_byte_map - (uintptr_t(low_bound) >> card_shift());
71 assert(read_byte_for(low_bound) == &_read_byte_map[0], "Checking start of map");
72 assert(read_byte_for(high_bound-1) <= &_read_byte_map[last_valid_index()], "Checking end of map");
73
74 _covered[0] = _whole_heap;
75
76 log_trace(gc, barrier)("ShenandoahCardTable::ShenandoahCardTable:");
77 log_trace(gc, barrier)(" &_write_byte_map[0]: " INTPTR_FORMAT " &_write_byte_map[_last_valid_index]: " INTPTR_FORMAT,
78 p2i(&_write_byte_map[0]), p2i(&_write_byte_map[last_valid_index()]));
79 log_trace(gc, barrier)(" _write_byte_map_base: " INTPTR_FORMAT, p2i(_write_byte_map_base));
80 log_trace(gc, barrier)(" &_read_byte_map[0]: " INTPTR_FORMAT " &_read_byte_map[_last_valid_index]: " INTPTR_FORMAT,
81 p2i(&_read_byte_map[0]), p2i(&_read_byte_map[last_valid_index()]));
82 log_trace(gc, barrier)(" _read_byte_map_base: " INTPTR_FORMAT, p2i(_read_byte_map_base));
83
84 // TODO: As currently implemented, we do not swap pointers between _read_byte_map and _write_byte_map
85 // because the mutator write barrier hard codes the address of the _write_byte_map_base. Instead,
86 // the current implementation simply copies contents of _write_byte_map onto _read_byte_map and cleans
87 // the entirety of _write_byte_map at the init_mark safepoint.
88 //
89 // If we choose to modify the mutator write barrier so that we can swap _read_byte_map_base and
90 // _write_byte_map_base pointers, we may also have to figure out certain details about how the
91 // _guard_region is implemented so that we can replicate the read and write versions of this region.
92 //
93 // Alternatively, we may switch to a SATB-based write barrier and replace the direct card-marking
94 // remembered set with something entirely different.
95 }
96
97 void ShenandoahCardTable::initialize(const ReservedSpace& card_table) {
98 MemTracker::record_virtual_memory_type((address)card_table.base(), mtGC);
99
100 os::trace_page_sizes("Card Table", _byte_map_size, _byte_map_size,
101 card_table.base(), card_table.size(), _page_size);
102 if (!card_table.is_reserved()) {
103 vm_exit_during_initialization("Could not reserve enough space for the card marking array");
104 }
105 os::commit_memory_or_exit(card_table.base(), _byte_map_size, card_table.alignment(), false,
106 "Cannot commit memory for card table");
107 }
108
109 bool ShenandoahCardTable::is_in_young(const void* obj) const {
110 return ShenandoahHeap::heap()->is_in_young(obj);
111 }
112
113 CardValue* ShenandoahCardTable::read_byte_for(const void* p) {
114 CardValue* result = &_read_byte_map_base[uintptr_t(p) >> _card_shift];
115 assert(result >= _read_byte_map && result < _read_byte_map + _byte_map_size,
116 "out of bounds accessor for card marking array");
117 return result;
118 }
119
120 size_t ShenandoahCardTable::last_valid_index() {
121 return CardTable::last_valid_index();
122 }
123
124 // TODO: This service is not currently used because we are not able to swap _read_byte_map_base and
125 // _write_byte_map_base pointers. If we were able to do so, we would invoke clear_read_table "immediately"
126 // following the end of concurrent remembered set scanning so that this read card table would be ready
127 // to serve as the new write card table at the time these pointer values were next swapped.
128 //
129 // In the current implementation, the write-table is cleared immediately after its contents is copied to
130 // the read table, obviating the need for this service.
131 void ShenandoahCardTable::clear_read_table() {
132 for (size_t i = 0; i < _byte_map_size; i++) {
133 _read_byte_map[i] = clean_card;
134 }
135 }
136
137 // TODO: This service is not currently used because the mutator write barrier implementation hard codes the
138 // location of the _write_byte_may_base. If we change the mutator's write barrier implementation, then we
139 // may use this service to exchange the roles of the read-card-table and write-card-table.
140 void ShenandoahCardTable::swap_card_tables() {
141 shenandoah_assert_safepoint();
142
143 CardValue* save_value = _read_byte_map;
144 _read_byte_map = _write_byte_map;
145 _write_byte_map = save_value;
146
147 save_value = _read_byte_map_base;
148 _read_byte_map_base = _write_byte_map_base;
149 _write_byte_map_base = save_value;
150
151 // update the superclass instance variables
152 _byte_map = _write_byte_map;
153 _byte_map_base = _write_byte_map_base;
154 }